Plain-English breakdown
NEC 200.7 provides several methods:
6 AWG or smaller: common methods include a continuous white or gray outer finish, or three continuous white or gray stripes along the full length on insulation other than green. Additional permissions cover specific applications.
4 AWG or larger: insulated grounded conductors may also be identified at installation with distinctive white or gray marking at terminations. The marking must encircle the insulation.
Flexible cords: use a white or gray outer finish or another method permitted by 400.22.
Multiconductor cables: Exception No. 1 to 200.7(E) permits reidentification at terminations during installation using distinctive white or gray marking or other equally effective means.
Why it matters
Under 200.7(D), grounded conductors of different nominal voltage systems sharing a raceway, cable, box, auxiliary gutter or enclosure must be distinguishable by system. The identification method must be documented and readily available, or permanently posted where those systems' conductors originate. For example, assigning white to one system and gray to another can distinguish them, using methods permitted for the conductor size and wiring type.
Do
Coordinate the identification method across drawing notes, conductor schedules and field markings.
Document how different voltage systems will be distinguished where 200.7(D) applies.
Do not
Treat white tape as blanket permission to reidentify any conductor.
Assume existing gray insulation proves a conductor is grounded; the informational note warns of past use on ungrounded conductors.
Field tip
Have qualified personnel verify conductor function, size, wiring type and markings using appropriate safe work practices before accepting existing wiring for reuse. Next: #041, 200.8 White/Gray Insulation and Permitted Reidentification, Part 3 of 4.
Questions to settle before design
What conductor sizes and wiring types are involved?
Will more than one voltage system share a raceway, box or enclosure?
Where will the identification method be documented or posted?
MasterBuild field checklist
Use qualified personnel and appropriate safe work practices before accepting existing wiring.
Do not assume gray insulation means a grounded conductor; verify the function.
Check that field markings match the documented identification method.
MasterBuild recommendation: process steps for design and site review, not code text.
Where MasterBuild helps
Existing-building electrical reviews and recertification, or send your project background. The fee is quoted in writing before work starts.
Code basis and applicability
Study edition: NEC 2026 (NFPA 70). Florida enforces NEC 2020 under the 2023 Florida Building Code (8th Edition). The 9th Edition (published; state adoption pending) adopts NEC 2023 for permit applications on or after 12/31/2026. Section numbers and some rules differ between editions. Verify the edition that governs your permit. Educational reference to NEC 2026 Section 200.7. Check the complete NFPA 70 text, the locally adopted edition and amendments, the authority having jurisdiction, and the selected equipment instructions before project use.